• Nuclear Engineering and Technology
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• 제50권1호
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• pp.116-125
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• 2018

Modified 9Cr-1Mo ferritic steel is a preferred material for steam generators in nuclear power plants for their creep strength and good corrosion resistance. Austenitic stainless steels, such as type 316LN, are used in the high temperature segments such as reactor pressure vessels and primary piping systems. So, the dissimilar joints between these materials are inevitable. In this investigation, dissimilar joints were fabricated by the Shielded Metal Arc Welding (SMAW) process with Inconel 82/182 filler metals. The notch tensile properties and Charpy V-notch impact toughness properties of various regions of dissimilar metal weld joints (DMWJs) were evaluated as per the standards. The microhardness distribution across the DMWJs was recorded. Microstructural features of different regions were characterized by optical and scanning electron microscopy. Inhomogeneous notch tensile properties were observed across the DMWJs. Impact toughness values of various regions of the DMWJs were slightly higher than the prescribed value. Formation of a carbon-enriched hard zone at the interface between the ferritic steel and the buttering material enhanced the notch tensile properties of the heat-affected-zone (HAZ) of P91. The complex microstructure developed at the interfaces of the DMWJs was the reason for inhomogeneous mechanical properties.

• 한국결정성장학회지
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• 제26권3호
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• pp.126-130
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• 2016

Ti-합금은 낮은 밀도, 낮은 탄성계수, 우수한 고온강도, 내산화성 및 인체적합성으로 자동차와 항공산업 및 바이오 산업에서 구조용 재료로 널리 연구되고 있다. 본 연구에서는 Ti-합금 중 대표적인 조성인 Ti-64(6 wt% Al, 4 wt% V) 합금에 대한 결정학적 특성과 미세조직에 대해서 알아보고자 하였다. XRD 분석을 통하여 Ti-64 샘플의 주요 결정상을 분석하였고, FE-SEM 및 EDX 분석을 통하여 Ti-64 합금 샘플의 미세구조를 화학조성의 차이에 의해 고찰하였다.

• 한국유체기계학회 논문집
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• 제19권4호
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• pp.35-38
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• 2016

A PFA lined ball valve, which is machined with fluorinated resin PFA to its inner part for improving corrosion resistance, non-stickness, heat-resistance, has been widely used in semiconductor/LCD manufacturing processes with the high purity chemicals as working fluid. Due to the safety concerns, the experiments for measuring the flow coefficient of a PFA lined ball valve should be conducted with water at room temperature according to IEC standards. However, it is required to know the real flow coefficient with the real working fluid, because the flow coefficient is critical to correctly design valves in piping system. In this study, we calculated the flow coefficient of a PFA lined ball valve 40A with hydrochloric acid ($40^{\circ}C$ 36% HCl) as the working fluid using a commercial CFD package, ANSYS CFX v15. The computational results had a good agreement with the measured data and showed a little difference between water and hydrochloric acid as the working fluid of a PFA lined ball valve.

• Nuclear Engineering and Technology
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• 제49권4호
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• pp.744-751
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• 2017

The fatigue crack propagation behaviors of Z3CN20.09M duplex stainless steel (DSS) were investigated by studying oxide films of specimens tested in $290^{\circ}C$ water and air. The results indicate that a full oxide film that consisted of oxides and hydroxides was formed in $290^{\circ}C$ water. By contrast, only a half-baked oxide film consisting of oxides was formed in $290^{\circ}C$ air. Both environments are able to deteriorate the elastic modulus and hardness of the oxide films, especially the $290^{\circ}C$ water. The fatigue lives of the specimens tested in $290^{\circ}C$ air were about twice of those tested in $290^{\circ}C$ water at all strain amplitudes. Moreover, the crack propagation rates of the specimen tested in $290^{\circ}C$ water were confirmed to be faster than those tested in $290^{\circ}C$ air, which was thought to be due to the deteriorative strength of the oxide films induced by the mutual promotion of oxidation and crack propagation at the crack tip. It is noteworthy that the crack propagation can be postponed by the ferrite phase in the DSS, especially when the specimens were tested in $290^{\circ}C$ water.

• 대한기계학회논문집A
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• 제40권12호
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• pp.1027-1035
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• 2016

내식성과 기계적 성능이 우수한 316L 스테인리스 강의 저주기 변형률제어 피로시험에서 3가지 변형률진폭과 3가지 변형률비의 조건이 피로수명에 미치는 효과를 분석하였다. 낮은 변형률범위에서 곡선이 거의 중첩되는 Masing 거동이 나타나고, 높은 변형률범위에서 비선형거동 응력범위가 서로 크게 벗어나는 non-Masing 거동과 함께 평균응력의 감소가 나타났다. 소성 변형률에너지를 이용하여 저주기 피로수명을 예측하고 non-Masing 거동을 고려한 수명예측 방법의 정확성 여부를 검토하였다. 각각의 변형률진폭과 변형률비의 조건에서 초기 수 사이클 동안 반복경화 현상 후 장시간동안 점진적으로 낮아져 연화하다가 파괴 되었다. 저사이클 피로수명을 정확히 예측하기 위해서는 변형률진폭에 따라 Masing 및 non-Masing 거동을 구분하고, 이를 반영한 수명예측식을 적용해야 함을 알았다.

• 폴리머
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• 제24권3호
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• pp.382-388
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• 2000

이온전도도가 높으며 균일하고 또 기계적 강도와 전기화학적 안정성이 우수한 전해질막을 얻기 위하여 poly(vinylidenefluoride-hexafluoropropylene) (PVdF-HFP) 공중합체를 전해질의 지지체로 선택하고, LiClO$_4$ 염이 포함된 ethylene carbonate (EC)와 ${\gamma}$-butyrolactone (GBL)의 흔합용매를 사용하여 겔-전해질을 제조하였다. 다양한 조성의 겔-전해질에 대하여 이온전도도, 열분석 및 선형주사전위 실험을 수행하였다. 이온전도도는 30PVdF-HFP+7.8LiClO$_4$+62.2EC/GBL 전해질막에서 3.8$\times$$10^{-3}$ S$cm^{-1}$ /로 가장 높았다. 열분석 결과에서 대부분의 시료는 대략 10$0^{\circ}C$ 정도까지는 안정하였으며, 특히 염은 고분자 사슬과 민감하게 반응하여 PVdF 결정질의 고온용융점을 낮추는 건을 확인하였다. 리튬 금속과 전해질 사이의 부식에 의해 생성된 부동태막에 의해 계면저항이 시간에 따라 계속적으로 증가하는 것을 확인하였으며, anodic stability는 대략 4.5 V vs. Li까지 안정한 것으로 측정되었다.

• Journal of Welding and Joining
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• 제26권5호
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• pp.49-59
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• 2008

Hastelloy C-276, corrosion resistant alloy at high temperature, is used in chemical plant and power generation industry. In this study, process parameter of laser welding for welding property in Hastelloy C-276 using a continuous wave Nd:YAG laser was studied. As the result of experiment, laser welding did not show segregation or crack at heat affected zone compared to conventional GTWA welding. The melting zone showed cell dendritic structure along with welding line. In addition, planer front solidification is occurred from welding structure, and it was progressed to cellular solidification. Optimal process parameter for butt welding was 1.2kW and 2.0 m/min for laser power and welding speed, respectively. While heat input, output density, tensile stress, and longitudinal strain was $441.98{\times}103$ J/cm2, $29.553{\times}103$ W/cm2, 768 MPa, and 0.689, respectively. Lap welding of the same material showed greater discrepancy in tensile property during 1 line and 2 line welding. For 1 line welding, tensile stress was about 320 MPa, and 2 line showed slightly larger tensile stress. However, strain was decreased by 20%. From this result, lap welding of the same material, Hastelloy C-276, with 2 line welding is considered to be more effective process than 1 line welding with consideration of mechanical property.

• 열처리공학회지
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• 제34권5호
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• pp.233-238
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• 2021

The mechanical, anti-tarnishing, and corrosion characteristics of Yuggi (Cu-22wt%Sn) alloy are greatly affected by fraction of constituent phases according to heat treatment method. The Yuggi heat-treated at 750℃ has a β1' phase of 98% or more, which is a high-temperature disordered beta phase, on the other hand, cast Yuggi that Sn is solid-solutioned into Cu consists with α-phase over 60v/o. This difference of constituent phases of Yuggi may cause a difference in dissolution of Cu under antimicrobial test condition. Nonetheless, few studies have been conducted on the effect of fraction of constituent phases and constituent phases in antimicrobial activity. In addition, few studies have also been conducted on the suitable method measuring the antimicrobial activity of Yuggi. Hence, the purpose of this study is to provide an optimum measurement method of antimicrobial activity, and to evaluate quantitatively the effect of constituent phases on antimicrobial activity.

• Korean Chemical Engineering Research
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• 제57권2호
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• pp.172-176
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• 2019

저생 미생물 연료전지(BMFC)는 바다나 호수의 뻘 속에서 저생미생물이 유기물을 분해하면서 발생시키는 전기를 이용한 연료전지다. 본 연구에서는 BMFC 전극으로 카본 소재를 발수 처리한 고분자 전해질 연료전지(PEMFC)의 가스확산층(GDL)을 사용해서 성능이 높게 나오는 구동조건을 찾고자 하였다. 높은 저항 값을 갖는 외부저항을 사용했을 때 성능이 높았으며 바닷물에서 리드선의 부식에 의한 전극과 접촉저항 증가를 피해야 성능을 유지할 수 있었다. 기포 발생기를 사용해 최고출력밀도를 2배 이상 높일 수 있었고 최적 구동 온도는 $40^{\circ}C$였다.

• Tribology and Lubricants
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• 제35권1호
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• pp.1-8
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• 2019

Demand for plastic gears are increasing in many industries due to their low production cost, light weight, applicability without lubricant, corrosion resistance and high resilience. Despite these benefits, utilizing plastic gears is limited due to their poor material properties. In this work, DLC coating was applied to improve the tribological properties of polyamide66 gear. 0 V, 40 V, and 70 V of negative bias voltages were selected as a deposition parameter in DC magnetron sputtering system. Pin-on-disk experiment was performed in order to investigate the wear characteristics of the gears. The results of the pin-on-disk experiment showed that DLC coated polyamide66 with 40 V of negative bias voltage had the lowest friction coefficient value (0.134) and DLC coated PA66 with 0 V of negative bias voltage showed the best wear resistance ($9.83{\times}10^{-10}mm^3/N{\cdot}mm$) among all the specimens. Based on these results, durability tests were conducted for DLC coated polyamide66 gears with 0 V of negative bias voltage. The tests showed that the temperature of the uncoated polyamide66 gear increased to about $37^{\circ}C$ while the DLC coated gear saturated at about $25^{\circ}C$. Also, the power transmission efficiency of the DLC coated gear increased by about 6% compared to those without coating. Weight loss of the polyamide66 gears were reduced by about 73%.